Protection valve device



Sept. 17, 1946.

G. T. MCCLURE PROTEGTIONVALVE DEVICE Filed March 15, 1945 INVENTOR, Glenn McCZu're BY ATTURNEY Patented Sept. 17, 1946 PROTECTION VALVE DEVICE Glenn T. McClure, McKeesport, Pa., assignor to The Westinghouse Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania Application March 15, 1945, Serial N0. 582,934

(Cl. 30S-84) 11 Claims. 1

This invention relates to fluid pressure brakes, and more particularlyto an air brake equipment of the type employed on a railway locomotive. i

Diesel-powered locomotivesfor certain classes of railway service in some instances comprise a plurality of individual power'units coupled together. For example, a complete Diesel locomotive may consist of one A (control) unit coupled to first and second B (auxiliary) units, all three power units carrying engine equipments controlled from the A unit. Diesel locomotives of `this class are operative to exert great tractive effort. particularly` at low speeds. Although such Diesel locomotives are regularly operated to great advantage and` without undue risk of separation of the several units, actual experience has demonstrated that suchV an accident is possible, and that the leading portionof a Diesel locomotive might break away from the other units and the rest of the train. The engineer stationed in the leading portion may in fact be unaware that a break-in-two has occurred, by reason of the enormous power which that unit delivers, and as a result, the parting of the main reservoir pipe between the separated units of the locomotive may seriously impair his control of the brake equipment, The locomotive brake equipment on a multiple unit Diesel locomotive is, of course, designed to operate automatically upon parting of the brake pipe to effect an emergency applica- `tion of the brakes, but if the engineer is unaware of a break-in-two and consequently allows his brake valve to remain in running, position, and if, as is usually the case, the controlled emergency feature of the equipment has been set for freight service to permit only a slow rate of brake cylinder pressure development, the loss of main reservoir pressure through the broken main reservoir pipe will in a short time seriously limit the brake cylinder pressure obtainable in the leading portion of the locomotive.

It is an object of my invention to provide an improved locomotive brake equipment designed for Diesel units of the above identified class, including means operative to prevent brake failures of this nature.

Another object of the invention is to provide an improved protection `valve device operative to prevent complete loss of main reservoir pressure in the leading locomotive in case of a train break-inftwo.

Another object is to provide an improved pro'- tection valve device operative to supply fluid under pressure from the main `reservoirs of the trailing locomotive units to those of the leading locomotive unit in the event that the compressor on the leading unit should fail. l Y

A further object is to provide means operative to permit the flow of fluid under pressure from the main reservoirs on the first locomotiveunit through the main reservoir pipe to the reservoirs on the trailing locomotive units only after the uid under pressure in the reservoirs on the first locomotive unit attains a selected degree of prese sure and operative thereafter when the uid pressure in the main reservoir pipe is reduced to a chosen lower degree to prevent the flow of iiuid under pressure from the reservoirs on the rst unit to the main reservoir pipe, which means maybe readily installed in an existing` brake equipment for cooperation with standard brake controlling devices without impairing the normal functioning of the apparatus. l 1 v- Other objects and advantages will be apparent in the following more detailed description of the invention. l'

The single figure in the accompanying draw'- ing is a diagrammatic view, partly in section, of a protection valve device constructed in accord-'- ance with the invention and associatedwith such portions of the air brake equipment of a` multiple unit Diesel locomotive as concern the inventtion. A

In the drawing, the reference numerals I and 2 indicate a pair of main reservoirs which are carried on the leading locomotive unit and comprise a part of the usual air brake equipment (not shown) thereon. The main reservoirs land 2 are connected by means of a pipe 3 vto apr tection valve device 4, which device operates to control communication between the pipe 3 and a main reservoir pipe 5, as will hereinafter more fully appear. A check valve device 6 is` provided to prevent a back flow of fluid under` pressure from the main reservoir 2 to the pipe 3, the main reservoir 2 being provided for the purpose of storing fluid under pressure to be supplied by way of pipe 'l to the usual air brake equipment (not shown) installed on the leading unit of a Diesel locomotive. The main reservoir pipe 5 comprises a section 8, carried on the leading 1ocomotive unit, Aand a section 9 carried on the trailing locomotive unit, the sections 8 and 9 being connected by a coupling means I 0. The

section 9 is connected'to another main. reservoir l I which comprises a part of the usual air brake equipment (not shown) for the trailing locomotive unit. It` willbe understood that the main reservoirs l and 2 are adapted to be charged with uid under pressure delivered by way of a pipe I2 from a compressor (not shown) mounted on the leading locomotive unit and the main reservoir II is adapted to be charged with fluid under pressure from a suitable compressor (not shown) mounted on the trailing locomotive unit.

The protection valve device 4 may comprise a base structure I3 supporting a casing structure I4 and containing a, supply chamber |.5 which chamber'i-s in constant4v open communication with the main reservoir I by way of the pipe 3'. Contained in the supply chamber I5 is a supply control valve I6, which valve cooperates with a valve seat I1, formed on the end of a bushing I8, tv control communication by way of said bushing between the supply chamber I and a passage I9.,

which passage connects with thel main reservoir pipe 8.

Formed in the casing structure I4 is a strainer and check Valve chamber 20, which chamber is in constant open communication with the supply chamber I5 by way of a passage 2I and with a diaphragm chamber 23 by way of a-passage 22. For the protection of the passage 22 against the passing` of dirt therethrough there is provided in chamber a wire screen strainer 24 which is clamped between two sectionsof the casing structurev I 4f. Also contained in the chamber 2u is a ball check valve 25 arranged for operative engagement with a valve seat 26 formed in a suitable bushing 21' mounted in the casing structure I4,

the under side of thecheck valve 25 being in communication with the passage I9 by way of a passage 28 and a chamber 29. For the protection of Ythe valve device 4 and the other air brake equipment when iiuid under pressure from the main reservoir pipe 5 flows past the check valve 25, as will hereinafter more fully appear, a tubular air cleaner or' strainer 30 of the cartridge type is mounted in the chamber 29-so as to have its inner peripheryA open to the passage 28 and its outer periphery exposed to the passage I9. Upon re'- l moval of a cap nut 3I which closes the outer end of the chamber 29 and hassealing engagement with one end ofthe strainer 30, the strainer may be readilyl removedv for cleaning.

Clamped at its periphery between two sections ofthe' casing structure I4 is a flexible diaphragm 32 having at: its upper side the chamber 23, which chamber is constantly open to the chamber- 28 by way of the passage 22'A and, as shown, maybe connected to'a piston chamber 33 byY way of a Valve chamber 34. and` a. passage 35, they passage 35. beingV open to atmosphere also by way of a choke- 3B?. At; the, under side of' thel diaphragm is a. spring chamber 31 which i's constantly open to atmosphere by way.y of-a passage 38.

Contained in the valve chamber 34 is a valve 39A having a fluted': stem 40 which extends through a suitable. bore in the casing so that itslower endY may be operativelyA engaged by the diaphragmv 32. Interposed between and operatively engagingy a cap nut 42| at the top of the chamber 34 and' the; valve 39 is a springY 42 which urges said valve toward its seated position.

Contained: in the,` chamber 31I andV interposed betweenl a diaphragmv follower 43 and a spring seat; member 424 isl aL compression spring 45, which, asY will hereinafter more fully appear, serves to establish they degrees of fluid pressure in the supply chamber I5 at: which the Valve I6 will be opened or closed'. The` follower 43 is slidably guided-in an annular member 46, the member .46 Aalso serving as amedium for clamping the dia- 4 V between a surface 41 of the member 46 and a shoulder 48 provided in the peripheral wall of the chamber 31, as shown Yin the drawing.v

The spring seat member 44 slidably engages a stud portion 49 of the follower member 43 for the purpose of retaining the spring -in operative engagement with the follower 43 and also for limiting, in a manner to. be explained later, the upward travel ofV a pistongmember 50 mounted in the chamber 33. The member 44 i's'substantially tubular inshape having its upper end 5I turned inwardly forV engagement with a washer `52 secured to' the stud portion 49 to thereby limit the downward movement of the member 44 and having'its lower end 53 ared outwardly for suppQrtI'lgj andretaihing the spring 45 at its lower end. f

.The piston member 5I] is substantially cupshaped for accommodating the lower ends of the spring 45 and seat member 44 and abuts the bottom surface of kthe seat member for propelling the same upwardly until the upper end 5I thereof engages the follower 43.. A'sealing ring 54 is pro'- Vided in an annular groove in the periphery of through bushing 56 in a` wall in the casing struc- Y ture I 4 and extends transversely through thepassage I9 andv bushing I8 into the supply passage I5. The stem is also provided with a sealing' ring' 51 for preventing leakage of iiuid under pressure between the passage I9 andV chamber 33. Secured by means of a pin 58 and a retaining spring or clip 59 to the lower end -of the stem 55 of the piston member 5U is the valve I5 which, asl will' later appear, may be operated thereby into engagement with the valve seat I 1. It is preferred that the clearances in the mounting means of the valve I Ii beisuflicient to permitthe valve tov be self-aligning in its operation.

In charging the locomotive with fluid under pressure and' under normal conditions, uid under pressure is supplied from the usual compressor (not shown) on the leadinglocomotive to the main reservoir I by' way of theV pipe I2 and iiows therefrom by wayy ofthe pipe 3, check valve de*- vice 6, and a pipe 60 to the main reservoir 2, from which fluid under pressure is supplied by way of pipe 1 to the usual air brake control equipment found on the leading unit of' a Diesel locomotive. Fluid under pressure also flows from pipe 3 through a passage 6I to the supply chamber I5 of the protection valve device 4. At the same 'time' fluid under pressure is also supplied to the main reservoir I`I on the trailing unit by the operation of auxiliary compressor meang` (not shown) mounted' on that'unit. Y

Fluid under pressure supplied to the chamber I5 of the protection valve device 4 flows from that chamber by way of the passage 2l to the chamber 28, thence by way of a choke 62, in'- serted in passage 22 for reasons which will appear later, and the passage 22 to the diaphragm chamber 23, whence it will flow past the fiuted stem 40 and valve 39 to the piston chamber V33 by way of the passage 35. Fluid under pressure being supplied to the pistonchamber 33 will also iiow to atmosphere by way of choke 35 at a, restricted. rate. The valve I6 being unseated as shown at initial charging', fluid under pressure in'cham'ber I5 may-'also lflow to main reservoir II by Way of the bushing I3, chamber I9 and main reservoir ,ls'eat I1. 50 acts through the medium of its stem 55 and `cation between chambers 23 and 33.

pipe 5, if the iluidpressure in the main reservoir II islower, such `as when the compressor (not shown) on the trailing unit is not operating.

Since the degree of iluid pressure in the chambers 23 and 33 is substantially the same and, the

effective area of the piston member l) is greater than that of the diaphragm 32, the piston member 5I] will respond to a lower degree of uid pressure than will the diaphragm 32. It will here be understood that the relative flow capacities of chokes B2 and 3B are such that the flow of fluid under pressure through choke 52 will be sufficient `to maintain the fluid pressure acting on the pis ton member 53 at approximately that of the main reservoir against the flow of fluid under pressure to atmosphere through choke 33. When `the pressure of fluid in the chamber 3.3 has reached a chosen degree (22 pounds for example) l as determined by the valve of the spring 45, the

piston member 56 will move the spring seat member 44 upwardly against `the opposing pressure of the spring 45 until the valve I5 engages the valve With this movement the piston member `the pin 58 to move the valve I6 into sealing engagement with' the valve seat I'I, closing communication between the chambers I5 and I9 and thus between mainreservoir I and main reser- However, fluid under pressure will continue to flow from chamber I5 to chambers 23 and 33 by the route previously described. When the pressure of fluid in the diaphragm chamber 23 has attained a higher chosen degree, such as 100 pounds, the diaphragm 32 will deflect downwardly in response thereto, causing the follower 43 to move downwardly until stopped by the engagement of the lower outer` surface thereof with the shoulder 48 in the chamber 3l. It should be noted that the spring 45 had previously been compressed a certain amount due to the upward movement of the piston member 58,' consequently `theforce of the spring acting to oppose the downward deflection of th'e diaphragm was correspondingly increased.

Upon the deflection of the diaphragm 32 to its lower position the spring 42 will act to move the valve 39 from the position in which it is shown4 .to its lower seated position, closing commmuni- This is the normal position for valve 39 on a leading unit with the brake equipment thereof fully charged. Fluid under pressure in the piston chamber 33 and the passage 35 will continue to now to atmosph'ere by way of the choke 36, thereby reducing the fluid pressure in chamber 33. When the pressure of uid in the chamber 33 acting on the `lower side of the piston member 50 decreases below the pressure of the spring 45 acting on the upper side of the piston member, the springwill `act to move the piston member downwardly to the position in which it is shown in the drawing.

The downward movement of the piston member `will cause the valve I5 to assume the position in which it is shown, this being the normal position 4for `valve I6 on a leading unit with the brake equipment thereof fully charged. Communication is again established between the main reservoir I on the leading unit and the main reservoir 1 I I on the trailing unit by way of pipe 3, passage 6I, chamber I5, bushing I8, passage I3 and main reservoir pipe 5.

It will be understood that th'e volume of the passage 35 and the chamber 33 is relatively small and that consequently the choke 35 will cause It will be apparenttherefore that substantiallyV the full force of the spring 45 will be effective at once to open the valve I6 promptly.

It should be further explained that any temporary uid pressure vdrop in the chamber I5, which' might be caused by the sudden opening of the valve I6, especially with a high pressure differential across it, will not, due to the how restricting choke (i2,v result in a corresponding reduction in the pressure of fluid in diaphragm chamber 23, thus insuring against anlundesirable operation of the diaphragm 32 and the piston member 53 to again close the valve i6. Thus the choke 62 serves to stabilize the diaphragm so that communication from the main reservoir I to the piston chamber 33 is maintained closed :and the communication from main reservoir I to the main reservoir I I `is maintained open against accidental movement. i

If, however, the main reservoir line` 5 is broken or opened to the atmosphere as by the accidental separation of the locomotive units, fluid under pressure in the main reservoir I will flow to atmosphere by way of the pipe 3, protection valve device il, and the undesired rupture in the main reservoir pipe 5. The resulting reductionin the fluid pressure in chamber I5 of the valve device 4 will cause fluid under pressure to flow from the `diaphragm chamber 23 by way of passage 22,

choke 62, chamber 23 and passage 2| to chamber i5 and thence to atmosphere by way of bushing I3, passage I3 and main reservoir pipe 5. When the pressure of fluid in chamber 23 has been reduced to some chosen low degree such as eighty pounds, the predominant pressure of the spring 35 will cause the diaphragml32 to deillect upwardly and act through the medium of the stem d to move the valve 39 against the opposing pressure of the spring 42 to itsunseated position in which it is shown in the drawing.

With the valve 39 unseated, fluid under pressure in diaphragm chamber 23, and consequently fluid under pressure in chamber I5 connected to chamber 23 by way of passage ZI, chamber 2l), choke G2 and passage 22, will flow to the piston chamber 33. In response to the fluid pressure acting on the piston member 5I), the piston mem^ ber will move upwardly against the opposing pressure of the spring 45. This movement of the piston member will cause the valve IIS to again engage the valve seat I'I, thus preventing further loss of fluid under pressure from the mainV reservoir I by way of pipe 5.

The reduction` in the pressure of fluid inthe main reservoir I will cause the compressor on the leading locomotive unit to start operating in the usual manner. This action in combination with the closing of the valve I5 might, if the choke 52 were not employed, cause a rapid increase in the fluid pressurein the diaphragm chamber 23 causing the valve 43 to seat and the valve I6 to open again before the fault causing the loss of fluid under pressure had been corrected. There 'would then follow another reductionv in fluid Lpressure and a consequent rapid pumping action.

This rapid pumping action is obviated yby the effect of the choke 62 in the passage `22 which delays the pressure build-up in the chamber 23 and thereby lengthens the time interval between the closing and opening of the valve IS.

As previously noted, the effective area of` the piston member 53 is considerably greater than that of the diaphragm 32. For this reason and also because chamber 33 is at atmospheric pressure 4and the pressure of the spring 4.5 has been reduced by the upward movementI of Athe diaphragm, Ythe piston member will exert a force greatly in excess of that required to propel the valve I6 to its seated position. This excess of force is desired to insure the seating of the valve leven though it or the valve seat I'I might be dirty .and :covered with sludge which usually accumulates in the communicating pipes of a fluid pres- .,sure brake system.

Assuming now that the compressor means on :the leading locomotive unit has been rendered `inoperative and that the compressor means on the trailing unit is operating to supply fluid under pressure to the main reservoir I I, the various parts of the protection valve device 4 will be in the positions in which they are shown in the drawing. Fluid under pressure in the main reservoir II will flow therefrom to the main reservoir I by way of the main reservoir pipe 5, passage I9, bushing I8, chamber I5, passage 6I and pipe V3 until the exemplary 22 pounds are reached, at

which ytime the valve I6 will be operated to its `seated position in the same manner as hereinlbefore described for 22 pounds of main reservoir pressure during the initial charging of the locomotive.

. However, although the flow of iiuid under pressure above 22 pounds from the main reservoir II to the main reservoir I is interrupted at valve I6, this flow `will continue from passage I9, and reservoir II, 'by Way of strainer 3G in chamber 29, passage 28, past ball check valve 25, chamberZI, passage 2I, chamber I5, passage 6I and pipe 3. When a uid pressure of 100 Ypounds is attained in the main reservoir I and a camber 23 of the protection valve 4, the same operation for unseating the valve I6 will take place as previously described in connection with the initial charging Of `the locomotive.

It will thus be seen that the greatest possible protection for the braking means on the leading unit of the locomotive against loss of fluid under pressure is provided by the protection valve device 4 embodying the invention. It prevents the passing of fluid under pressure from the first main reservoir to the main reservoir pipe until operating pressures with a marginal degree of safety `fluid pressure supply to the rst main reservoir `should fail and fluid Vunder pressure is available in any of the trailing units, the protection valve device will then operate to supply Iluid under pressure from the main reservoir pipe to the rst main reservoir. Upon attaining safe operating pressures in the rst main reservoir, the protecting valve device will again function to retain those ypressures if the uid under pressure in the main reservoir pipe is being depleted beyond a safe degree.

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. The combination with a fluid conducting conduit normally charged with fluid under pressure, of a valve device comprising a casing having two communicating passages constituting a portion of said conduit, a valve operative to open and close the communication between said passages, movable abutment means for actuating said valve and operative in response to fluid pressure for closing said valve, a spring urging the'movable abutment in ya direction for opening -said valve, and valve means for controlling communication between one of said two passages and said movable abutment means, said valve means being responsive to a reduction in iluid Apressure in vsaid one passage to a predetermined degree to open the latter communication and responsive to an increase in fluid pressure in said one passage to a predetermined higher degree to close the latter communication.

2. The combination with a fluid conducting conduit normally charged with uid under pressure, of a valve device comprising a casing having two communicating passages constituting a portion of said conduit, a valve operative to open` and close the communication between said passages, movable abutment means for actuating said valve and operative in response to luid'pres'- sure for closing said valve, a spring urging the movable abutment in a direction for opening said valve, valve means for controlling communication between one of said two passages and vsaid movable abutment means, said valve means being responsive to a reduction in uid pressure in said one passage to a predetermined degree to open the latter communication and responsive to an -increase in fluid pressure in said one passage to a predetermined higher degree to close the latter communication, and means for reducing the lpressure of fluid acting on said movable abutment means.

3. In a fluid pressure flow control valve device comprising a casing having two connected passages through which uid under pressure may flow from one section of a fluid conduit to :another spaced section of the conduit, a valve mounted in said casing and operative to one position to close communication between said `passages and operative to another position to open communication between said passages, means responsive to the pressure of fluid in one of said passages for actuating said valve to its closed position and responsive to a reduction in the pressure of fluid acting thereon for actuating said valve to its open position, a second Valve having a position for establishing communication through which the fluid under pressure in said one passage may be supplied to said means and having a position for closing said communication, a movable member responsive to an increase in fluid pressure in said one passage toa chosen degree for eiecting .the operation of said second valve to its communication closing position and responsive to a reduction in the 'uid pressure in said one passage for effecting the operationrof said second valve to its communication establishing position, and means for reducing the pressure of fluid acting on said means. Y

4. In a fluid pressure flow control valve device having two connected passages adapted to establish communication between two uid conducting conduits, a valve operative to one position lto close the connection between said passages and operative to another position for opening the communication between said passages, means operative by uid under pressure from one of vsaid passages for actuating said valve to close the connection between said passages and operative upon a reduction in the pressure ,of uid supplied thereto for-actuating said valve to open the connection between said passages, valve means responsive to variations in the pressure of Afluid in said one passage for controlling the pressure -of iluid acting on the rst mentioned meansa passage by-passing sald valve and leading from the other of said passages to said one passage through which fluid under pressure may flow from said other passage to said one passage when said valve is Iclosed, and means interposed in the by-pass passage 4for preventing the ow of fluid therethrough from said one passage to said other passage. A I Y 5. In a Vfiuid pressure flow control valve device having `two connected passages adapted to establish communication between two fluid conducting conduits, a valve operative to one position to close the connection between saidfpassages and operal tive to another position for opening` the connection between said passages, means operative by fluid under pressure from one of said passages for actuating said valve to close the connection between said passages and operative upon a reduction in the pressure of fluid supplied thereto for actuating said valve to openthe connection between said passages, valve means responsive to variations in the pressure of fluid in said one passage for controlling the pressure of ;uid acting on the rst mentioned means, a passage by-passing said valve and leading from the other ofsaid passages to said one passage through which fluid under pressure may ow from said other passage to said one passage j when said valve is closed, means interposed in the by-pass passage for preventing the ow of fluid therethrough from said one passage to said other passage, and fluid cleaning means interposed in the by-pass passage at a point located between said other passage and the last mentioned means.

6. The combination with a iluid conducting conduit of a iluid pressure flow control valve device comprising a casing having two fluid flow connecting passages constituting a portion of said conduit, a valve operable to open and close the iiuid flow connection between said passages, means responsive to fluid pressure foroperating said valve to close said connection and responsive to a reduction in fluid pressure for operating said valve to open said connection, means for reducing the fluid pressure acting on the first mentioned means at a relativ'ely slow rate, and valve means operative to supply fluid under pressure from said one passage to the rst mentioned 4 means to effect the operation to close said valve and operative in response to a certain degree of fluid pressure acting thereon to interrupt said supply, thereby causing the rst mentioned means to operate said valve to open said connection, said valve means being conditioned as an incident to the opening of said valve to respond to a degree of fluid pressure acting thereon lower than said certain degree for again supplying fluid under pressure from said one passage to the rst mentioned means.

7.' The combination with a fluid conducting conduit of a fluid pressure iiow control valve device comprising a casing having-two fiuid ilow connecting passages constituting a portion of said conduit, a valve operable to open and clos-e the fiuid flow connection between said passages, means responsive to liuid pressure for operating said valve to close said connection and responsive to a reduction in fluid pressure for operating said valve to open said connection, means for reducing the fluid pressure acting on the first mentioned means at a relatively slow rate, valve means operative to supply uid under pressure from said one passage to the irst mentioned means to effect the operation to close said valve and operative in responsive to a certain degree of fluid pressure acting thereon to interrupt said supply, thereby causing the first mentioned means to` operate said valve to open said connection, said'valve means being conditioned as an incident to the opening of said valve to respond to a degree of fluid pressure acting thereon lower than said certain degree for again supplying fluid under pressure from said one passage to the rst mentionedmeans, means for controlling the rate at which fluid is supplied to said valve means to prevent the pressure in said valve means from being varied prematurely.

A3. The combination with a fluid conducting conduit, ofga fluid pressure iiow control valve device comprising a casing having two connected `passages constituting Va portion of said conduit, a valve operable to open and close the connection between said passages, a movable member responsive to iiuid pressure for operating said valve to close said connection and responsive to a reduction in the fiuid pressure for operating said valve to open said connection, means for reducing the iluid pressure acting on the movable member at a relatively slow rate, and valve means responsive to variations in the pressure of fluid in said one-passage to control the supply of fluid under pressure from said` one passage to said movable member and thereby the uidpressure acting on said movable member, said valve means being operative in response to a `cer,v tain degree of fluid pressure to supply fluid under pressure to said movable member to eiect the operation of said valve to close said connection and being conditioned as an incident to the connection closing operation of said valve to be operative at a degree of fluid pressure higher than said certain degree to interrupt the supply of fluid under pressure from said one passage to said movable member.

9. The combination with a fluid conducting conduit, of a fluid pressure flow control valve device comprising a casing having two connected passages constituting a portion of said conduit, a valve operable to open and close the connection betweenV said passages, a movable member responsive to fluid pressure for operating said valve to close said connection and responsive to a reduction in the fluid pressure for operating said valve to open said connection, means for reducing the fluid pressure acting on the movable member at a relatively slow rate, valve means responsive to variations in the pressure of iluid in said one passage to control the supply of fluid under pressure from said one passage to said movable member and thereby the uid pressure acting on said movable member, said valve means being operative in response to a certain degree of fluid pressure to supply fluid under pressure to said movable member to effect the operation of said valve to close said connection and being conditioned as an incident to the connection closing operation of said valve to-be operative at a degree of fluid pressure higher than said certain degree to interrupt the supply of ud under pressure from said one passage to said movable member, and means for restricting the rate at which fluid under pressure is supplied to the valve means to prevent the pressure of fluid in said valve means from increasing at such a fast rate as to cause the valve means to operate prematurely to interrupt said supply.

10. In a uid pressure brake system comprising a plurality of uid pressure reservoirs interconnected by means of a common conduit in which system it is `desired to maintain fluid in 11 one reservoir at pressures above a chosen degree, aprotection valve device interposed vbetween said one reservoir and 4said conduit comprising ya casing having two connected passages one of which is connected to said one reservoir and the other to said conduit, a valve operative to one position to close the connection between said passages and operative to another position to open the connection between said passages, va movable member responsive to fluid' pressure Vfor operating said valve to -close said connection and responsive to a reduction in theiuid pressure for operati-ng said valve to open said connection, means for reducing the vfluid pressure acting on the movable member at -a relatively slow rate, valve means responsive to varia-tions in the pressure of fluid lin said one passage to control the supply of fluid under pressure from V'said one passage to sa'id movable member and 4thereby the fluid pressure 'acting on said movable'member, said valve means being operative in response to 'a -certain `degree of lfluid pressure to supply uid under pressure to-said movable lmember to effect the operation of Vsaid valve yto close said connection and lbeing conditioned -as an incident to the connection clos-ing operation of'said valve to be operative at -a degreeof uid pressure higher than said V`certain degree to interrupt the supply 'of uid under pressure from said 4one -passage vto said movable member, `and a unidirectional -ow comme passage psf-*passing said valve throughfwhieh iluid under pressure may ow vfrom said other passage to said one passage.

11. In a fluid vpressure brake system comprising a plurality of 'fluid pressure main reservoirs interconnected by means of la Vcommon conduit in which system it 'is desired `to maintain Yiiuid inone reservoir at pressures Within a chosen range, a vprotection valve dev-ice interposed between said reservoir and said conduit 'comprising a casing having one passage 'open to said conduit and another passage open to said one reservoir, a valve controlling communication between fsaid passages, piston means lconnected vto said valve and 'operative .to `one-position to close "said fva'lv-e in response toa constant supply of fluid at a pressure above a certain chosen degree and operative to another'position upon the interrup-` tion of said supply to 'open said Valve, and valve means open for supplying fluid'under pressure from said one reservoir to said piston means, said valve means being -conditonable by said piston means when in vsaid yone position to respond to an increase in uid pressure 'to a, predetermined degree above said chosen degree to close said communication and to respond to a decrease -in fluid pressure to a certain predetermined lower degree tovopen said communicat-ion.

GLENN T. 

